Given the remoteness of the off-campus stations, BDSN data acquisition
equipment and systems are designed, configured, and installed
so that they are both cost effective and reliable. As a result, the need
for regular station visits has been reduced.
In 2006-2007 the focus of BSL's technical efforts went toward maintaining and repairing existing instrumentation,
stations and infrastructure that was put in place during the early and mid 1990's .
While expanding the data acquisition network remains one of the long term goals of BSL, it is equally important to assure integrity of the established network and preserve data quality.

The broadband seismometers installed by BSL are of the first generation and are now approaching 25 years in age. Concurrently, the first generation of broadband dataloggers are now 17 years old. Computer systems are retired long before this age, yet the electronics that form these data acquisition systems are expected to perform without interruption.

SUTB:
During 2006-2007, the BSL has received support from the TA for operating permanent stations in northern California. The BSL has provided telemetry for this TA site for the past year and a half. Data are delivered to the BSL datacenter via a radio telemetry link to the BSL station ORV. Beyond the initial setup and deployment, this has involved maintaining the radio telemetry between the seismic site and the radio repeater - a distance of several kilometers. The radios inexplicably lost their connections and control programming several times during the past year. In each instance, they could be reinitialized remotely from Berkeley, and telemetry resumed. Some of this year's support was used for equipment maintenance and to correct telemetry problems. BSL engineers visited both the radio installation and the seismic vault at the TA site, Sutter Buttes (SUTB), many times to maintain and troubleshoot network connectivity.

KCC: At station KCC (Kaiser Creek California) BSL engineers removed the STS-1 seismometers during 2006-2007 and installed an STS-2, and instrument consistent with the specifications of the TA. This provided the opportunity to use the three STS-1 components from Berkeley in the STS-1 electronics upgrade program (REF). During this testing, one of the STS-1 sensors was found to have reduced sensitivity. The instrument was repaired and is scheduled to be reinstalled before the winter of 2007, when the STS-2 is removed.

WENL: The BSL station WENL began operating in 1997. The equipment is installed in a high humidity adit used for storing and aging wine. BSL engineers replaced cables and the STS-2 seismometer this year after a reduction in the instrument's sensitivity (signal levels) was observed. Since WENL was installed, growth and development at the winery caused increases in the background noise levels over the past several years. A search for a suitable replacement site has begun.

HOPS:
The BDSN station at Hopland, California, has been operating since October, 1994. The station is located approximately 100 miles northwest of Berkeley. During the current year, BSL engineers visited the station seven times to remove, repair, and replace seismometers and the geodetic GPS (BARD) receiver.

Actual repair of instruments in the field is difficult due to the nature of the sites, lack of test equipment, poor lighting, etc. In most cases, BSL engineers will remove failed equipment and replace it with a working spare in a single trip. The objective is to minimize the station down time. In the case of HOPS, which is close to the BSL, we elected to remove the equipment, return it to the Berkeley lab, repair it, and in at least one case, replace it the following day.

At HOPS, all three components of the STS-1 seismometers were found to have degraded sensitivity. Experience with the site, where similar problems have occurred in the past, led to the suspicion that the insulation on the connectors on the seismometer electronics had broken down. The connectors were replaced.

Later in the year, the prototype of the new STS-1 electronics (MetroZet) was installed at HOPS. As described elsewhere in this report, these electronics have the advantage of swept sign and step calibration functions over the network connection. The field operation of these electronics is currently being evaluated at HOPS.

SAO:
At SAO, BSL engineers began rebuilding the seismometer vault in late summer of 2006. The area in front of the vault was excavated and re-graded to improve drainage. A new concrete entrance was poured, and most importantly, a welded steel security door was added. The wooden door it replaced had been broken into on a number of occasions during the past ten years.
A second steel door was hung on the outside to create a secure atrium and thermal buffer for the vault. As envisioned, future seismic instruments could be added in this atrium. Back-filling the entrance, final re-grading and cleanup of the site will be completed before the winter of 2007. SAO was built in 1966 and upgraded to first generation Quanterra broadband recording in early 1992.

MCCM:
Two site visits were required to MCCM during the 2006-2007 year. During the first of these, a failed 12 vdc power supply was replaced. Later in the year, VSAT telemetry was restored during the second visit. A present, BSL engineers have developed a plan to improve continuous telemetry using digital radio link. Permits have been acquired for the installation of the necessary radios, repeater radios and infrastructure.

YBH: Station YBH was visited three times in the past year.
Power at YBH is supplied by the local utility company. In this heavily forested area, it is BSL's obligation to keep the path to the power meter clear of fallen trees. One trip was necessary to remove fallen trees. In a later trip, BSL engineers replaced a failed data acquisition subsystem belonging to the CTBTO. The third trip was also necessary to resolve CTBTO telemetry issues. BSL's YBH station has been providing data to the CTBTO since 2002.

HUMO:
BSL engineers visited the station at HUMO once during 2006-2007. This visit was necessary to repair and replace the power supply for the VSAT equipment. HUMO is the BDSN station furthest from Berkeley.

OXMT: The OXMT site has been providing borehole seismic and strain data, as well as geodetic GPS data, since February of 2004. This is a mountaintop site within 6 kilometers of the coast. During the past year, BSL engineers replaced a DC power supply which appeared to have failed due to weather-related problems.

SBRN:
The site SBRN is a companion to OXMT and also provides borehole seismic and strain data, as well as geodetic GPS data. The site is within 100 meters of an elementary school. During the past year, the GPS monument and cover were vandalized and subsequently replaced by BSL engineers.

RFSB:
BSL engineers made four trips to the Richmond Field Station (RFSB) during the past year.
In two instances, the telemetry ports from the data logger were found not to be working, presumably as a result of a power surge or a nearby lightning strike. The other two trips were necessary to investigate and troubleshoot low signal levels on the surface accelerometer. Corroded connectors were found and replaced in each case. The RFSB site is within one kilometer of the San Francisco Bay.

MONB:
The MONB site lies on an east/west ridge north of San Jose, California. BSL operates a geodetic GPS and telemetry equipment there. In 2006-2007, BSL engineers installed radio equipment to consolidate data from future sites in the valley below. We expect to add at least one GPS site with data telemetry through MONB in the next year.

SCCB:
During October of 2006, BSL engineers replaced the strong motion accelerometer at SCCB. The previous instrument (Kinemetrics FBA-ESP) was rendered unusable when the instrument enclosure was flooded during seasonal rain. A MetroZet accelerometer was installed in its place.

ORV:
BSL engineers visited the station at ORV during the past year to replace the back up batteries. The replaced batteries were 15 years old and at end of their manufacturers specified lifetime.

BRIB:
In March of 2007, BSL engineers installed a fiber optic local loop (between the telephone company demarcation and the instrument vault) at BRIB. The fiber optic data connections provide the advantage of electrical isolation from the telephone system, while concurrently allowing greater telemetry speeds and additional telemetry paths. This work was undertaken in part to support the Stanford/USGS electro-magnetic and magnetic monitoring equipment which was installed at BRIB during the past year. The Stanford/USGS instruments telemeter data to the BSL data center for archival.

BDM: The Quanterra data logger at Black Diamond Mine (BDM) froze several times during the past year and remained unresponsive. In each case, however, the data logger was rebooted remotely from Berkeley and did not require a site visit.
At this time, BSL is permitting with the East Bay Regional Parks to add a geodetic GPS to the other instruments on site. As planned, the monument would be located within 100 meters of the seismometers.